Lieutenant Governor Brian E. Schatz (Democratic) was appointed to Hawaii's Class 3 U.S. Senate Seat on 26 December 2012. On 4 November 2014, he was elected in a Special Election to fill the remainder of the term.

Senator James W. "Jim" DeMint (Republican) resigned from South Carolina's Class 3 U.S. Senate Seat on 2 January 2013.

Congressman Timothy E. "Tim" Scott (Republican) was sworn to South Carolina's Class 3 U.S. Senate Seat on 3 January 2013. On 4 November 2014, he was elected in a Special Election to fill the remainder of the term.

Senator John F. Kerry (Democratic) resigned from his Massachusetts Class 2 Senate seat on 1 February 2013 following his confirmation as Secretary of State on 29 January 2013.

Interim Senator William M. "Mo" Cowan (Democratic) was appointed to Massachusetts' Class 2 U.S. Senate Seat on 1 February 2013 and sworn in on 7 February 2013.

Senator Frank R. Lautenberg (Democratic, New Jersey) passed away on 3 June 2013 at the age of 89 from complications of pneumonia.

Senator Jeffrey S. "Jeff" Chiesa (Republican) was appointed to New Jersey's Class 2 U.S. Senate Seat on 6 June 2013.

Senator Edward John "Ed" Markey (Democratic) was elected to Massachusetts' Class 2 U.S. Senate Seat in a Special Election on 25 June 2013 and sworn in on 16 July 2013.

Senator Cory A. Booker (Democratic) was elected to New Jersey's Class 2 U.S. Senate Seat in a Special Election on 16 October 2013 and sworn in on 30 October 2013.

Senator Max Sieben Baucus (Democratic) resigned from his Montana Class 2 Senate seat following his confirmation as Ambassador to China on 6 February 2014.

Senator Tom Coburn (Republican) announced his resignation from his Oklahoma Class 3 Senate seat effective at the end of the 113th Congress.

Senator John Walsh (Democratic) was appointed to Montana's Class 2 U.S. Senate Seat on 7 February and sworn in 11 February 2014.

Political PartiesParties appear in parenthesis and italics when a candidate receives the endorsement of a given Party and/or official sources indicate a candidate's association with a particular Party but only where the Party in question does not appear on the actual ballot as such.

Candidates for office appear on this page in italics where 'The Green Papers' does not yet have independent confirmation from a legal election authority that the person has been officially certified to appear on the ballot.

When available, we post each candidate's FEC identification number, the date of their most recently filed Report of Receipts and Disbursements, their "Tot" [Total Receipts (contributions received or what came in: FEC Form 3, Line 16, Column B)] and their "Dsb" [Total Disbursements (expenditures or what was spent: FEC Form 3, Line 23, Column B)]. A link is provided to the Federal Election Commission's Summary Report for those who might wish to explore the details.

If a candidate raises or spends $5,000 or less, he or she is not subject to FEC reporting requirements.

Class 1 seats begin their terms at noon on 3 January 2013 and end their terms on 3 January 2019. The next regular election for these seats is in 6 November 2018.
Class 2 seats begin their terms at noon on 3 January 2009 and end their terms on 3 January 2015. The next regular election for these seats is 4 November 2014.
Class 3 seats begin their terms at noon on 3 January 2011 and end their terms on 3 January 2017. The next regular election for these seats is 8 November 2016.

Article I, Section 3, clause 2 of the Constitution of the United States reads as follows:

"Immediately after [the Senate of the United States] shall be assembled in Consequence of the first Election, they shall be divided as equally as may be into three classes. The Seats of the Senators of the first Class shall be vacated at the Expiration of the second Year, of the second Class at the Expiration of the fourth Year, and of the third Class at the Expiration of the sixth Year, so that one third may be chosen every second Year..."

Pursuant to this Constitutional provision, a three-Senator Committee was appointed by the Senate on 11 May 1789 to come up with a plan to carry out the requirements of that provision; this Committee reported to the Senate on 14 May 1789 a plan to divide the then 20 Senators (there were 10 of the 13 original States represented in the Senate at the time- each having 2 Senators: North Carolina and Rhode Island had yet to ratify the U.S. Constitution, while New York had so ratified but had failed to elect Senators as of that date) into the requisite three electoral Classes: under this plan, three groups of Senators (set up in such a way so as no State had its two Senators in the same group) were to be listed and the first Senator on each list (a list which was set up geographically north-to-south in the manner in which the Electoral Vote for President was counted before Congress at that time, so that two of the first Senators on these lists were from New Hampshire and the third was the first Senator in alphabetical order from Massachusetts) was to each blindly draw a piece of paper numbered either "1", "2" or "3" out of a box in the possession of the Secretary of the Senate. This plan being agreeable to the Senate and so approved, the drawing of lots in this manner was carried out the following day (15 May 1789)- such lot drawing ultimately determining that, to start with, Classes 1 and 2 were to have 7 Senators each and Class 3 was to have only 6 Senators.

When New York finally seated its two Senators during the ensuing Summer, there was another lot drawing (actually a double-lot drawing) on 28 July 1789 to determine the Classes for these seats: since one of the seats had to be Class 3 to make it equal in number to that of the other two Classes so far, the two New York Senators each blindly drew between two pieces of paper, one marked "3", the other which was blank- after this, there was a second lot drawing in which the New York Senator who had drawn the blank paper blindly drew again between two pieces of paper marked "1" and "2": he drew "1" so that New York would henceforth have Senators of electoral Classes 1 and 3.

When North Carolina seated its two Senators after ratifying the Constitution on 21 November 1789, there was yet another lot drawing (on 29 January 1790) in which North Carolina's two Senators each blindly drew between pieces of paper marked "2" and "3" (since there were now 12 States and, thus, 24 Senators: 24 being equally divisible by 3, there would now have to be 8 Senators in each of the three Classes to fulfill the Constitutional provision that, as nearly as was practicable, one third of the Senate be elected every second year).

After Rhode Island- the last of the 13 original States- finally ratified the Constitution on 29 May 1790 and subsequently seated its two Senators that Summer, there was yet one more lot drawing in the First Congress (on 25 June 1790) in which Rhode Island's two Senators blindly drew between pieces of paper marked "1", "2" and "3": one Senator drew "2", the other drew "1"- thereby determining electoral Classes 1 and 2 as those for the Senators from this State. When Vermont was admitted to the Union as the 14th state on 4 March 1791, there was again a double lot drawing as there had been for New York. From that day until this, whenever a new State has been admitted to the Union, these types of lot drawings (the type determined by the necessity of keeping the number of Senators in each electoral Class as close to one third as possible at the time of said lot drawing) between the new State's first Senators is held before the Senate to determine in just which of the three electoral Classes that State's Senate seats will be placed from then on.